Not so long ago I searched for a Spanish dub of a very popular anime and had a tough time finding active seeds on most sites listed on the Treasure Trove page.

I think YMMV depending on what you look for, and how old is it. I had much better results adding “Spanish” and “latino” to a simple google search. Turns out some people stream a single series on a website (as opposed to multiple series hosted on large streaming platforms).

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I’ve always went to animeflv.net, I haven’t been there in a long time tho, so I don’t know if the quality is the same.
For manga I’ve only consumed it in English, but tachiyomi has a lot of options for manga in several languages, you could check some of them.